Volume 21, Issue 2-3 -

Water is one of the key deterioration factors for porous building materials and has the capability of enhancing the deleterious effect of other factors such as air pollution and biocolonization, among others. The focus of the paper is the interaction of water with the porous inorganic materials: how does water enter the pore system, and how does it leave it? How does the presence of clays or soluble salts in porous materials affect these mechanisms? Pairwise examples are provided to illustrate the varying behavior of water in different materials. Also addressed is the importance of the pore size distribution on the behavior of water and its transport mechanisms. The aim of the paper is to synthesize the key points required to understand why water enters a porous system, in what way it is distributed within it, and the slow manner in which it departs, since time of wetness is fundamental in enhancing the effect of co-factors.

This study evaluates the suitability of electrical resistance-based moisture content measurements, which are known to guarantee reliable values for moisture contents of wood, when applied to selected mineral building materials with and without water-repellent treatment. For the testing specimens of cement – mortar and solid brick were produced – the water-repellent treatment for the mortar specimens was carried out both by internal hydrophobization and surface treatment, while the bricks were hydrophobized by surface treatment only. For the measurements of electrical resistance electrodes were inserted into the specimens. For this purpose a borehole was drilled and the measuring point at the tip of the electrodes was glued conductively into the material. The remaining outer part of the electrodes was sealed with electrically isolating glue in order to establish a conductive connection in the middle of the specimens only. After storage at different relative humidity, the electrical resistance of the specimens was recorded using data logging devices. Based on gravimetrically measured moisture contents resistance characteristics for each material were established. A satisfying accuracy resulting from the comparison between gravimetrically measured and mathematically calculated material moisture contents confirmed the suitability of electrical resistance based moisture content measurements for selected treated and untreated mineral materials.

High-performance fiber-reinforced cement-based composites (HPFRCC) can be characterized by low porosity and fine pores as compared to normal concrete and therefore this interesting material absorbs little water or aqueous salt solutions if exposed to aggressive environment. These properties are indications for excellent durability and long service life of structural members or structures made with this high-performance material. In practice, however, most structures and structural elements are designed to be load bearing. The influence of an applied tensile stress on capillary absorption was investigated and results are presented in this contribution. It was found that the coefficient of capillary absorption increases rapidly if a tensile stress exceeding half of the tensile strength is applied. This observation has to be taken into consideration if HPFRCC is to be applied in aggressive environment. The maximum admissible stress must be reduced accordingly.

Towards the end of the nineteenth century and the beginning of the twentieth century new technological evolutions and material developments gave rise to different modular structural flooring systems, which allowed light but strong floors to be constructed. This paper gives an overview of the evolution in flooring systems, their durability problems, and how to solve them. Similar systems also have been used for roof constructions. The strengthening of an atypical vaulted roof structure in the “Het Depot” theatre in Leuven, composed of terracotta arch and panel elements, showing its specific problematic and its specific revalorization approach serves as a case study to illustrate the methodologies applied.

Preventive Conservation is argued to improve preservation of heritage at large. The UNESCO chair on Preventive Conservation, monitoring and maintenance of monuments and sites (PRECOM 3 OS) has pushed research and collaboration to understand the nature of preventive conservation in the field of built heritage. The study of the concepts and practices of prevention in public health helps to understand the systemic nature of prevention and how they can be transferred to the conservation world.